I inquired about ordering it before a visit to Paris and I was told to place the order I would need to wire the funds for the bag at the time of the order. I didn't end up doing it because the main reason I wanted to place the order in advance was to give enough time for the luggage tag to be painted and completed. I found out that they were out of the luggage tags so there was no need to do it.
Someone else should pipe in here, but I think what they do is they ring up the order as a deposit, and then when you pick it up they change it a purchase allowing you to present that purchase receipt when leaving France.